Cases of the novel coronavirus are growing among workers at government agencies that oversee safety at airports and airlines, with the Federal Aviation Administration sending workers in a Chicago-area office home after an employee fell ill and the Transportation Security Administration disclosing a new case at the Atlanta airport.

These workers are at the agencies critical to keeping planes in the air and in many cases cannot do their jobs by telework. Officers with U.S. Customs and Border Protection, for example, have been on the front line in responding to the spread of the virus, charged with implementing new screening measures for Americans returning from Europe.

Over the weekend — the first since new travel restrictions affecting 28 European countries went into effect — it was a chaotic scene at some airports, with CBP officers and travelers packed together for what in many cases was an hours-long process.

Unions that represent the employees have accused managers of doing too little to protect their staffs, who interact closely with the public.

“The threats they face were made clear this weekend as CBP employees and thousands of travelers were needlessly and dangerously crowded together creating a situation ripe for transmission of the coronavirus,” said Tony Reardon, president of the National Treasury Employees Union, which represents CBP officers.

“Processing travelers at 328 ports of entry is not a telework-eligible job, and more should be done to protect them,” he said.

The virus’ spread has shaken the aviation system as nations across the globe take steps to limit travel and Americans cancel work trips and vacation plans. The main airline trade group said Monday that the industry might need more than $50 billion in government aid to weather the outbreak.

But after a weekend when major airports were engulfed in chaos, the acting leader of the CBP struck a cheerful tone in a tweet Monday.

Acting Commissioner Mark Morgan shared photos of officers helping passengers, wiping down work surfaces and standing alongside staff from the Centers for Disease Control and Prevention.

“Very proud of our CBP officers who quickly adjusted course this weekend, reduced wait times & never lost sight of their mission—keeping America safe,” Morgan wrote on Twitter. “I also appreciate our stakeholders’ patience & cooperation. The health & safety of the public & our workforce is our top priority.”

CBP did not respond to questions about the concerns raised by the union, nor did the Department of Homeland Security.

The FAA issued an internal emergency alert Monday, saying an employee in the office responsible for overseeing United Express and other airlines at O’Hare International Airport tested positive for the coronavirus.

The employee works at the FAA’s Chicago Certificate Management Office. Employees in that office perform inspections on Air Wisconsin Airlines, which operates as United Express, and also has crews based at Washington Dulles International Airport and in Milwaukee and Columbia, S.C.

The office, in Des Plaines, Ill., also oversees more than 50 foreign airlines, including those flying from O’Hare, Chicago Midway International, Chicago Rockford International, and airports in Milwaukee and South Bend, and Gary, Ind., according to the FAA.

United Airlines and Air Wisconsin Airlines did not immediately respond to questions about whether their employees may have had contact with the infected individual and if they are being quarantined or monitored.

As a result of the positive test, that and another office in the same building near O’Hare will be staffed with teleworking employees, the alert said.

The second office, the flight standards district office, houses aviation safety inspectors, maintenance inspectors, managers and technicians who make sure planes and airline operations are safe.

The FAA said in a statement that the agency is “working with the appropriate authorities to identify and locate people who might have come into contact with the employee in recent days. We provided co-workers with CDC guidance to self-monitor for signs of illness.”

The employee, an aviation safety inspector, was last in the office March 4, the agency said. It said the flight standards office “is open, but all employees are teleworking.” It said the certificate management office also remains open, with employees working from home.

The FAA said it has also coordinated with airlines about tracing contacts with the FAA inspector. It added that two other agency employees have tested positive for the virus, including an employee of the air traffic control program management office at headquarters in Washington and another employee who works for the Office of Finance and Management in a “full-time telework capacity” in the agency’s eastern region.

The TSA has created a website to disclose when its officers get sick, listing seven officers. The site provides basic information on when the officers last worked and what job they perform.

The Atlanta officer’s last shift was during the day on March 7. The airport was ranked the world’s busiest last year.

In a statement, the TSA said the officer was at home and receiving medical treatment. The agency said employees who interacted with the sick officer have been alerted and that it was working with the local health department “to monitor the situation as well as the health and safety of our employees and the traveling public.”

The agency has also said it is stepping up efforts to clean checkpoints and is allowing passengers to request that officers put on a fresh pair of protective gloves during screenings.

TSA is allowing passengers to carry 12 ounce bottles of hand sanitizer through security, relaxing its normal rules on liquids.

But because of ongoing problems in getting people tested for the virus, there could be gaps in the disclosures.

TSA officer Brian Shoup said he started feeling ill on Feb. 29. The first health-care provider he saw prescribed steroids and antibiotics, and he went back to work screening passengers before he started feeling worse and paid a visit to the emergency room.

“They went into panic mode,” Shoup said. “They did a really good job of taking care of me and protecting everybody in there. But the problem is, this is the underlying problem period, in Tennessee because of the lack of tests, they wouldn’t test me unless I was admitted.”

The hospital put Shoup under quarantine, and his wife — also a TSA officer — was eventually told to stay home too. But without a test result, Shoup won’t know for sure whether his illness was caused by the coronavirus and members of the public he came into contact with can’t be alerted to take extra precautions.

Because of how officers deal intimately with members of the public, Shoup said he thought they should be prioritized for testing: “Why are we not afforded these tests before sports figures or people of influence?”

The new screenings on arriving passengers were part of restrictions President Trump announced last week in a bid to slow the spread of the novel coronavirus from Europe, which has emerged as a new global hotspot for the disease. But travelers arriving over the weekend expressed surprise at how cursory the screening was for returning Americans.

The restrictions on travelers from 26 European countries went into effect at midnight Friday, with the measure expanding to Britain and Ireland on Monday. Americans can still return home from those countries but are being funneled to 13 airports set up to screen them.

Travelers arriving at Dulles International Airport Sunday, one of the designated airports, reported short waits, but only limited screening. One passenger showed a reporter a photocopied form asking for basic information on their health and where they had been. Another shared guidance from the CDC about staying home and keeping watch for symptoms of covid-19.

D.C. resident Nik Kowsar, 50, said he was surprised that the only question he encountered while passing relatively quickly through customs at Dulles after flying in from London was: “Do you have any health conditions to declare?”

“I thought they were going to be screening everyone and checking temperatures,” Kowsar said.

Kowsar said he had been scheduled to return home Tuesday, but moved up his flight Saturday night after seeing photos online of passengers stuck in crowded, hours-long delays at Chicago’s O’Hare airport Saturday as they awaited screening.

“The flight wasn’t that full last night, but there weren’t many empty seats, so many other people made that decision as well,” Kowsar said.

A CBP spokesman said the agency was using “a combination of traveler history records, officer questioning and observation, and self-declarations to identify travelers requiring enhanced health screening.”

Steve and Audrey Boyle, of Finksburg, Md. in Carroll County, said someone checked their temperature with a probe placed near their forehead after they landed at Dulles. They had arrived on a British Airways flight from London, but had filled out paperwork on the airplane saying they had been to Greece. Their cruise also had stopped in Egypt, Turkey, and Cypress, though they were not allowed to disembark in Israel.

Neither of them had a fever, and both said the health screening seemed sufficient.

“I think all they can do is check temperatures and notice if anyone is coughing or sneezing,” said Steve Boyle, 60, who works in construction.

“What else are they going to do?” added his wife, Audrey, 56.

She works part-time as a home health aide and said she planned to stay away from her elderly client for two weeks and would limit her trips outside her home, but would probably go to the grocery store.

“I don’t see myself staying in my house for 14 days,” Audrey Boyle said, “but I can see myself being very careful for 14 days.”

When Trump announced the restrictions last week, public health experts questioned their utility since the disease was already widespread inside the United States. Some passengers pointed out apparent holes in the system, including that they had eight or more hours on board a plane with travelers who had been in some of the worst affected countries, even if they themselves had not.

In a Twitter post late Sunday, Morgan said CBP had increased staffing to deal with the wait times.

Reardon, the union president, said the agency needed to share information from the CDC if it learned that a passenger had become sick after being screened by a CBP officer. He also called for officers to be allowed to use administrative leave if they need to self-quarantine, so as to not take a financial hit, and to be tested at the agency’s expense.

“By definition, their job may put them in harm’s way because they come in contact with international travelers around the clock,” Reardon said.